Liquid spray nozzles, from which jets or streams of various cross-sections issue in operation, in most cases produce a cohesive jet at the exit of the nozzle. The jet tends to break up into irregular packages of liquid after travelling over some distance through the ambient air (gas). The liquid packages usually break up further into droplets as they travel farther. The breakup of the originally cohesive stream is caused by a number of basic physical phenomena resulting in instabilities of such free jets and thus a loss of cohesion with a consequent division of the jet into isolated particles or droplets. Since spray nozzles are mostly intended for the generation of a directed "spray", i.e. a predetermined moving cloud of droplets, such nozzles have been designed to promote the jet breakup by various designs of the nozzle flow guiding structures and the nozzle exits. Additionally, jet breakup has been induced by externally imposed or internally generated vibratory effects, etc. In recent years, spray nozzles functioning on the basis of fluidic mechanisms have become known, these nozzles containing fluidic oscillators which generate oscillatory or sweeping jets at the exits of the nozzles. In these nozzles a motion usually transverse to the jet flow direction promotes the breakup into droplets.
In most situations it is desirable to generate droplet sprays as soon as possible after a jet issues from a nozzle, whether the spray is utilized to spray onto surfaces or whether it is intended to generate a cloud (the latter for example in gas scrubber applications). It is obvious that the sooner a jet is broken up into droplets after leaving the nozzle structure, the less distance is required between nozzle and the region where the droplets are intended to take effect, whatever such effect may be in a particular application.
Unfortunately, in spite of decades of design effort in the nozzle trade, most conventional nozzles issue an initially cohesive jet, albeit usually highly stressed by various mechanisms, which jet only gradually breaks up into droplets over some considerable distance downstream, depending on numerous factors. For instance, a conventional nozzle generates a jet which may not start to break up until some distance downstream from the nozzle exit which distance may be ten to a hundred or even a thousand times the width of the nozzle outlet opening. In general, higher supply pressures and thus higher flow velocities are required to effect earlier jet breakup. In many applications fluidic oscillator nozzles have allowed significant reductions in supply pressure requirements in comparison with conventional nozzles whilst generating the same or even improved spray performance and breaking up the stream issuing from the nozzle at shorter distances from it.
An early jet breakup into droplets is desirable for a number of reasons. For instance, spraying a wide angle fan spray onto a surface is generally very advantageous when the sprayed fluid has the shortest distance to travel before impact, because the sprayed liquid is least exposed to ambient conditions, does not dry out or evaporate as much, does not deflect as much if exposed to air currents, does not get contaminated as much, etc., all in comparison with conventional nozzle spray performance. Naturally, space and distance is at a premium in many applications, and a reduction in the spray nozzle distance requirements is a great advantage. Longer spray distances may also cause continuing breakup into smaller undesirable droplet sizes, loss of momentum and controllability, particularly in the presence of transverse wind or other gas currents, and may force higher pressures and thus higher power consumption than needed when an early jet breakup is facilitated.
The present invention improves such performance significantly in that it not only causes much earlier breakup, but it forces the jet to break up within the nozzle structure or at its exit before the fluid exits from the nozzle. Additionally this breakup is amenable to various design measures, as it is caused by structural influences within the nozzle. Therefore, a considerable degree of control of the breakup mechanism is offered by the present invention.